Connecting lights to a normally closed door trigger....

Discussion in 'The Projects Forum' started by AznGothic, Dec 23, 2013.

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  1. AznGothic

    Thread Starter Member

    Feb 17, 2008
    I am installing lights on a vehicle that has normally closed door triggers. The goal is to have the lights come on when you open the door and go off when you close the door. Normally I would just connect the ground side of the lights to the door trigger but this particular car goes to ground when you close the door and an open circuit when you open the door.

    My initial thought was to wire up an SPDT relay. I would have 12V going to 85, the door trigger going to 86. The power side of the lights would go to 30 and the negative side of the lights would ground to the body of the car. 87 would be open and 87a would go to 12V. This way when the door shuts, the relay comes on which opens the circuit and when the door opens the relay loses its ground on the coil thus closing the circuit to the lights and turning them on. I decided against this idea though because this would mean the relay would be on majority of the time and get hot plus drain the battery in the car.

    I found a schematic on wiring an aftermarket alarm into a normally closed door trigger which used a 10k ohm resistor on a 12V source that wired into the door trigger and into the alarm through a diode. From my understanding, when the door is closed you would have a direct ground which would draw the 12V away from the alarm and to the door trigger. When you open the door the only ground left would be the resisted ground in the alarm so the 12V would flow towards it and trigger the alarm. I decided to try using this schematic with a relay in place of the alarm. This would allow the relay to be off while the door is shut (since the 12V would move towards the door trigger) and the relay to be on when the door is open. It didn't work. With the resistor in place, the relay would not power up. I disconnected everything and just ran 86 to ground and 85 to 12V and the relay came on. So then I tried running 86 to ground and 85 to the 10k ohm resistor which was connected to 12V and the relay would not turn on.

    Am I missing something? Is the resistor to high? Can you not use a resistor in between your power source and the relay? Is there a better way for me to wire up these lights to turn on when the door trigger goes to open and turn off when the door trigger goes to ground? The relay is a standard SPDT 30/40A 12VDC relay that you can buy at any auto parts store. The lights are 7W each and there is one light per door (4 doors total). Each light should only come on when the corresponding door opens which is why I'm trying to use the door trigger.
  2. #12


    Nov 30, 2010
  3. bertus


    Apr 5, 2008

    I am closing this thread as it violates AAC policy and/or safety issues.

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